- 1 -MARINE ENGINEERING TEAMFLEET UPKEEP GROUPCategory :
Electricity DATE : 03/21/2012REF.NO. : 2012 - 001SEQ.NO. : 578
ESUBJECT: Blackout while passing through the Gulf of AdenA main
switchboard blackout occurred on an LNG vessel under our operation
while it was passing through the Gulf of Aden. The blackout
happened during maintenance work on the main switchboard. After the
blackout, electrical power was immediately restored, but the ship's
crew took approx. 5.5 hours to restore all systems, including the
main turbine. As a result, the ship was immobilized while it was in
the piracy area.Diesel propulsion ships may encounter the
occurrence of blackout similarly. To avoid a similar trouble, the
following should be confirmed as soon as possible: the condition of
each air circuit breaker (ACB), ACB operation, and emergency
procedures.Needless to say, the risk of marine casualties in
high-risk areas or during coastal navigation is higher than during
oceangoing navigation. Therefore, a risk assessment prior to
maintenance work should be carried out if the possibility of a
blackout exists.1. Summary of accident
Replacement of the malfunctioned HIMAP for the No. 2 turbine
generator fitted in the main switchboard (MSB).Function of HIMAP:
Power management of MSB, monitoring, and safety device for
6600V
0800 Commenced replacement of the HIMAP for the No. 2 turbine
generator fitted in the MSB.0820Transferred entire electric load
from the No. 2 turbine generator to the No. 1 turbine generator and
then disconnected the No.2 turbine generator.0836An alarm sounded
for the No. 1 main bus-tie breaker earth fault. Immediately after
the alarm, the alarm for the No. 2 main bus-tie breaker earth fault
also sounded. 0837 The No. 1 turbine generator was automatically
disconnected, causing - 2 -a blackout. The standby diesel generator
automatically started, and electric power was restored to both the
6600V high voltage (HV) switchboards. However, electric power was
not restored to the No. 1 440V low voltage (LV) switchboard because
the root ACB(TM1) of the switchboard was open. The cold start
boiler feed pump was notable to start because there was no power
from the No. 1 440 LVswitchboard. Worse, the main boiler was not
able to recover due to amalfunction of the uninterruptible power
supply (UPS) for the boiler.1022 The ACB (TM1) for the No. 1 440V
LV switchboard was manually closed and electric power was
restored.1345Both boilers were steamed up using emergency electric
power insteadof the damaged UPS, and preparation work for the main
turbine operation was completed.1359 Maneuvering operation
resumed.2. Blackout sequence (see attached Fig. 2)(1) During
replacement of the HIMAP, a live wire (terminal no. 18)
accidentally made contact with an adjacent connection (terminal no.
15).(2) The above momentary event would have caused a short circuit
and the circuit breaker (MCB-252) to trip. (3) There is a
transducer that monitors the voltage and frequency downstream from
MCB-252. It detected an abnormal condition.(4) The No. 1 turbine
generator was disconnected because of the No. 2 HV MSB low voltage
and frequency alarm, thus causing the blackout.3. Cause of extended
unrestored condition for No. 1 440V LV switchboard (see attached
Fig. 1)The latch relay for the ACB of the No. 1 440V LV switchboard
was not set in the "latch" position. Therefore, the ACB would not
close automatically. Moreover, much time was required to determine
that the ACB was in an open position. Normal setting>>>
Latch position Setting prior to the blackout incident>>>
Unlatch positionThe "unlatch" position of the latch relay is a
safety device used during maintenance work. If the latch relay is
set to the "unlatch" position, the ACB will not close
automatically. The latch relay might have been set to the "unlatch"
position when the previous inspection was conducted by the service
engineer.Latch relay for ACBBUS-TIEFig. 1GPT: Ground Potential
TransformerBUS-TIEFig. 2
